They unanimously adopted a declaration stating terrorism would not be allowed to destabilise Bulgaria and that presidential elections planned for later this month would go ahead.
Mr Lukanov, a former Communist who helped topple the former dictator Todor Zhivkov, headed the two Socialist governments that followed Mr Zhivkov's 35-year rule. He was ousted in late 1990 after strikes and demonstrations in protest at the slow pace of reform.
Although he remained an influential Socialist MP, Mr Lukanov subsequently turned his attention to business. He became a strong supporter of economic change and was critical of Bulgaria's current Socialist Prime Minister, Zhan Videnov, who has delayed introducing free-market reforms.
Between February and April, Mr Lukanov was under security service protection following a threat on his life, but the protection was lifted when investigators felt the case had been solved. Speculation was rife yesterday as to who could have been behind the murder - and to what end. Some argued that it could have been one of the mafia-style shootings that have plagued the country since 1989; others insisted the motive had to be political.
According to Georgi Apostolov, deputy editor of the independent Kontinent newspaper, the killing could have been carried out at the instigation of extremists with the aim of forcing a postponement of the presidential election and of providing a pretext for the imposition of martial law.